1. Field of the Invention
The present invention relates to an electromagnetic valve whose valving element is actuated by utilizing magnetic force of an electromagnet.
2. Description of Related Art
An example of a conventional normally-closed electromagnetic valve will be described. In the normally-closed electromagnetic valve, an electromagnet is produced by energization of a coil. A movable core is attracted to and contacts with a fixed core magnetized by the electromagnet, so that a valving element attached to the movable core is disengaged from a valve seat to cause the electromagnetic valve to be open. When the energization of the coil is stopped and magnetic force of the electromagnet disappears, the movable core is pushed back in an opposite direction from the fixed core by reactive force of a return spring, and the valving element is engaged with the valve seat, thereby to close the electromagnetic valve. In the above-described electromagnetic valve, for example, an elastic body such as rubber can be used for the valving element. In this case, by the repeated opening and closing operation of the valving element for a long period, plastic deformations such as wear and creep are produced in the valving element and the valve seat, so that the valving element and the valve seat are shaped to conform to each other. Thus, a sealing performance when the valving element sits on the valve seat is improved as time passes. However, if the movable core, to which the valving element is attached, rotates while the movable core is attracted and moves to the fixed core, the above-described portions of the valving element and the valve seat, which are conformed in form with each other, are relatively shifted from each other. Therefore, the sealing performance when the valving element sits on the valve seat cannot be maintained.
For the measures against this problem, a technology (see, JP2005-214225A, JP2005-98340A) is known. According to this technology, the movable core is attracted on radially one side of a cylindrical core guide part for guiding the movable core when the movable core is attracted and moves to the fixed core. In JP2005-214225A, the center of the return spring which urges the movable core is eccentrically arranged relative to the central axis of the movable core, so that the movable core is pressed against one side of the core guide part and rotation of the movable core is limited. In JP2005-98340A, a gap expansion part, which expands a gap between the movable core and the core guide part, is formed on an outer periphery of the movable core, or an attachment center of an impact absorbing means, which is attached to the movable core, is made eccentric from the center of the movable core. As a result, the movable core is pushed against one side of the core guide part, and rotation of the movable core is prevented.
However, in JP2005-214225A, because an action center of urging force of the return spring applied to the movable core is shifted from the center line of the movable core, a sealing load may be one-sided when the valving element sits on the valve seat, and leakage from the electromagnetic valve may occur. In JP2005-98340A, a gravity center of the movable core is shifted from the center line of the movable core, i.e., the gravity center is not located on the same line as the center line of the movable core. Therefore, in the electromagnetic valve disposed in a vehicle, for example, rotation of the movable core may be not limited due to its install direction, an acceleration of the vehicle, a centrifugal force and so on.